Appliance Design - July 2008 - (Page 23)

GAS TECHNOLOGY Fig. 1. Sequence of images demonstrates ability for hot-wire igniter to burn off contamination. Image at far left shows the element covered with ranch dressing, a thick liquid containing fats, water, sugars, and dairy products. The middle two photos occur during the energized phase. Smoke indicates contaminant burn-off and elimination. Photo on far right confirms successful burner ignition. bonding, or high-moisture environments. When this happens, the high voltage will find the path of least resistance to ground. This occurs most frequently through the wire connecting the high-voltage source to the electrode at the ignition point. This wire, which is required to be high-voltage rated by CSA or UL, is difficult to find in a high-temperature rating, precluding reliable usage in hightemperature applications, such as low NOx burner systems. In addition, as the spark ignition system ages, ignition tends to become less and less reliable. For European applications, the electromagnetic interference (EMI) generated by all high-voltage spark systems can be especially problematic for the design engineer. European standard EN 298 mandates system immunity to radiated EMI. This requirement can create many challenges for the product designer and require greater complexity for many ignition systems. Often, other electronic components in the appliance system can experience erratic operation due to EMI. This is a concern not only for OEMs exporting to the European market, as this require- ment may also make its way to the North American market in the near future. The next, and more recent stage in on-demand ignition history was the development of hotsurface ignition systems, which typically utilize a ceramic-based resistive element that heats up to ignition temperature when energized. One of the alluring attributes of traditional hot-surface systems is the amount of thermal mass that is available for natural gas ignition, which occurs at around 1,200 DegF, while propane ignites at about 900 DegF. Hot-surface technology provides a number of advantages over spark ignition, but also brings a new set of issues to the table that must be considered. A traditional hot-surface system typically uses 24 V or 120 V applied to the ignition element, which achieves adequate ignition temperature in roughly 30 seconds or more. This is much slower than spark ignition, where ignition occurs almost immediately, and the lag is mostly due to the thermal mass of the igniter that must be heated. The longer heat-up times may not be fast enough for some LLC Introducing the MM643KX The SmartValve™ Q3400 Replacement Silicon Nitride for your toughest application. Drop-in installation (OEM dimensions). Replaces hundreds of common applications. Contact us today for special pricing: * ANSI Standard, ANSI Z21.20, Automatic Electrical Controls for Household and Similar Use - Part 2: Particular Requirements for Burner Ignition Systems and Components. www.applianceDESIGN.com info@surfaceigniter.com www.surfaceigniter.com SPECIAL INTRODUCTION ON PAGE 25 applianceDESIGN July 2008 23 800-321-4147 http://www.surfaceigniter.com http://www.surfaceigniter.com http://www.appliancedesign.com

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Appliance Design - July 2008

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